This invention relates generally to a tensioner for yarn. More specifically, the invention relates to the progressive tensioning of a yarn from an essentially stress free condition to a condition of generally uniform tension.
Yarn tension devices are needed in many textile applications and a great variety of them have been used heretofore. In general, a yarn tension device includes some means for applying a retarding force to a linear movement of the yarn. Frequently in the past such retarding forces have for example been provided by friction surfaces and the present invention also is concerned with a yarn tension apparatus having friction surfaces for engaging a moving yarn.
Although the invention in some of its broader aspects may be applicable to various yarn tensioning needs in the textile field, it includes features of particular significance in connection with the task of elevating the tension level of a yarn from essentially zero to some substantial level suitable for winding the yarn onto a package. Such applications are particularly difficult ones from a number of aspects, and the apparatus must include a combination of features in order to be satisfactory.
On the one hand, the output yarn tension level must be generally uniform if the yarn is to be handled by conventional take-up or winding equipment. The conventional take-up machines usually are themselves provided with yarn tension devices of some sort but these typically are not intended to function efficiently in instances where there are very large tension variations in the output yarn. Hence, for an application where yarn is being removed from, for example, a pile and delivered to a winding machine, the interposition of an extra tensioning system is necessary in order that the yarn input to the winding machinery may occur at a generally uniform tensions level.
On the other hand, attainment of a reasonably uniform tension level must not interfere with the practical requirements imposed by the need to obtain high production rates. That is, the apparatus must be so constructed as to minimize down time and to operate at high linear yarn feed rates. Various known devices which seem, on a theoretical basis, appropriate for producing output tension uniformity, fail to accommodate satisfactorily these practical factors and they are not suitable for use in the type of commercial application for which the present invention has proved especially beneficial. For an example of such a device, reference may be made to U.S. Pat. No. 2,331,261.